Mn K-edge XANES spectroscopy of a photosynthetic O2-evolving complex. High-quality pre-edge features and distinct fine structures in the S1- and S2-states.
High-resolution XANES (X-ray Absorption Near Edge Structure) spectroscopy for Mn in the S1 and S2 states of the spinach photosynthetic O2-evolving complex revealed distinct features in K-edge spectra, when a high signal-to-noise (S/N) ratio of ca. 80 with a low and constant background-to-signal (B/S) ratio of 0.15 to 0.18 was attained. Six features resolved in each S-state spectrum involve a pre-edge feature due to 1s----3d transitions, a main-edge feature possibly due to 1s----4s transitions and four fine structures superimposed on the principal absorption bands due to 1s----4p* transitions. The high-quality pre-edge features were analyzed according to a parametric ligand-field theory in comparison with those of some typical authentic Mn complexes. It was deduced that i) all of the four Mn ions in the S1-state are octahedrally coordinated and two of them constitute a di-mu-oxo bridged Mn(III, III) dimeric subunit; ii) the bridged Mn(III) ions are further bridged by a deprotonated water dimer, (HOHOH)-, and coordinated by imidazole-N and carboxylate-O- on the opposite side of the Mn atom from the di-mu-oxo bridge; iii) the other two Mn ions exist in the form of Mn(III) monomeric subunits; and iv) upon the S1----S2 transition, only the bridged Mn(III,III) is oxidized to Mn(III,IV). The distinct change in the principal absorption band shape upon the S1----S2 transition is briefly discussed to obtain the XANES evidence for a tetrameric Mn-cluster.
Kusunoki
M
M
School of Science and Technology, Meiji University, Kanagawa.
Ono
T
T
Matsushita
T
T
Oyanagi
H
H
Inoue
Y
Y
D002462:Cell Membrane; D008024:Ligands; D008345:Manganese; D010100:Oxygen / Q000378:metabolism*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000378:metabolism; D010944:Plants / Q000032:analysis*; D011188:Potassium; D011487:Protein Conformation; D013052:Spectrometry, X-Ray Emission; D013816:Thermodynamics
D008024:Ligands; D045322:Photosynthetic Reaction Center Complex Proteins; D008345:Manganese; D011188:Potassium; D010100:Oxygen